2 Experiments on American and Foreign Building Stones. 
and decay, have been able to sustain themselves in high, bold, 
naked, angular cliffs, unprotected by soil, and yet unfurrowed by 
irregular disintegration, are manifestly those to which the engi- 
— _iheer and architect are to direct their attention, when they seek = 
. materials for durable works of art. On the other hand, they will 
- shun those rocks which the causes above enumerated have kept 
constantly down to a level with the ground, or which barely rise 
in some few patches to the surface, and are there seen disintegra- 
ting, scaling away, and covering themselves with a soil derived 
_ from their own debris. 
_ * he chemistry of geology furnishes to the architect and en- 
gineer most important hints for guiding their selection of materi- 
als; hints which when taken with other tests and proofs, leave 
them without excuse for choosing those of an inferior character. 
The influence of such a substance as iron pyrites on the durabili- , 
‘ty of rocks in which it occurs, is so well known to every one ac- 
- quainted with even the rudiments of geology and mineralogical 
chemistry, as scarcely to need a formal statement.* ff 
of carbonic acid with water in dissolving carbonate of lime, and 
the readiness with which it acts on loosely aggregated crystalline 
masses of that carbonate, to effect their disintegration, may be 
understood from any elementary work on chemistry. e great- — 
er solubility of sulphate than of carbonate of lime may be ascer- 
tained from the same source. The weakness of coarsely crystal- 
lized stones as compared with those of finer texture, is so well — 
known as to be properly classed among the canons of architecture.t 
Of all the purposes for which building materials are employed, | 
that which requires the utmost attention to durability is the erec- 
tion of national monuments. It is a mockery to the dead, an 
an opprobrium to the living to put perishable materials into struc- 
tures professing to perpetuate the virtue of great and good men 
The Spanish nation is represented to have recently determined 
on the erection of a magnificent statue of bronze to rest on a — 
base of rose granite, the most enduring of that species of rock, 
to commemorate the glory of Columbus. ices 
The question of the strength of a material to resist a crushing 
ad 
ae ee 
oe Maat 
~~ 
oks to the relation between the cohesion of a material and its 3 
pacity to resist the action of other than mechanical causes of 
"| *«Pyrites when present (in granite) renders the rock unfit for use, as it decom- 
_ poses and stains or rusts the surface, besides loosening the grains and causing 
_ Fock to fall to pieces.”—Dana’s Mineralogy, p. 579. 
Borgni’s “ Constructions Diverses,” p, 23, and Rondelet’s “ Art de Batir.” 
i x 
